This project seeks to investigate two critical questions in child language acquisition: (1) WHEN do toddlers show evidence of grammatical productivity in comprehension? (2) HOW does this productivity emergence vary, both cross-linguistically (i.e., do children learning some languages demonstrate earlier emergence than children learning other languages?) and within a given language, across grammatical constructions (i.e., do some grammatical constructions yield earlier emergence of productivity than others?)? This project addresses these questions by bringing together two usually-separate strands in language acquisition research. First, this will be one of the first studies of children's early grammatical productivity to take a cross- linguistic approach, focusing on three languages which have been selected to enable multiple types of comparisons. Second, this will be one of the first cross-linguistic studies of early grammatical knowledge to have comprehension at its core, as children's emerging productivity will be assessed via the intermodal preferential looking paradigm (IPL). Children's early grammatical productivity in verb morphology and syntax will be assessed in English, French, and Turkish. These languages vary most obviously in their reliance on word order (English) versus verbal inflections (i.e., clitic pronouns; French) versus nominal inflections (Turkish) for marking argument structure in the basic clause. Four sets of experiments, which investigate the acquisition of language-specific argument structure will be conducted. These ask when children demonstrate productivity with word order (Study 1), verbal morphology relevant to thematic relations (Study 2), noun case markings (Study 3), and structural bootstrapping (Study 4). Comparisons will be made across languages for each experiment and across experiments for each language. This research could reveal when children's language abilities become adult-like in one important way. Its focus on comprehension and its comparison of different languages could reveal how the age of this ability depends on the task (understanding rather than speaking) and the language being learned. This research thus could provide information about language- and task-specific milestones for assessing children with language disorders. [unreadable] [unreadable] [unreadable]